Piston follower device

ABSTRACT

A piston follower device for control applications characterized by a control piston disposed in a control chamber and having a fluid passageway therethrough for communicating outside the control chamber; and a pilot piston disposed in a pilot chamber and having a regulator surface portion that is positionable adjacent the end of the fluid passageway that is in fluid communication with the control chamber to control the size of a fluid outlet. A port is provided in the pilot chamber for connecting the pilot pressure end with a first source of pressure for developing a force to position the pilot piston. A port is provided in the power end of the control chamber that, in coaction with the flow outlet, effects a control pressure for positioning the control piston and opposing the force on the pilot piston. A spring is disposed to act on the pilot piston, tending to force it in one direction or the other toward an equilibrium position. Also disclosed are specific applications in which the fluid ports are connected with sources of pressure for control applications; such as, positioning a valve portion with respect to a valve seat; and in which the equilibrium position effects s fully opened valve or a fully closed valve.

United States Patent Johnston 15] 3,656,706 [451 Apr. 18, 1972 [54]PISTON FOLLOWER DEVICE [72] Inventor: Everett E. Johnston, Newark, Tex.

[73] Assignee: Esco Elevators, Inc., Fort Worth, Tex.

Primary ExaminerArnold Rosenthal Attorney-Wofford and Felsman [5 7]ABSTRACT A piston follower device for control applications characterizedby a control piston disposed in a control chamber and having'a fluidpassageway therethrough for communicating outside the control chamber;and a pilot piston disposed in a pilot chamber and having a regulatorsurface portion that is positionable adjacent the end of the fluidpassageway that is in fluid communication with the control chamber tocontrol the size of a fluid outlet. A port is provided in the pilotchamber for connecting the pilot pressure end with a first source ofpressure for developing a force to position the pilot piston. A port isprovided in the power end of the control chamber that, in co-action withthe flow outlet, effects a control pressure for positioning the controlpiston and opposing the force on the pilot piston. A spring is disposedto act on the pilot piston, tending to force it in one direction or theother toward an equilibrium position. Also disclosed are specificapplications in which the fluid ports are connected with sources ofpressure for control applications; such as, positioning a valve portionwith respect to a valve seat; and in which the equilibrium positioneffects s fully opened valve or a fully closed valve.

11 Claims, 3 Drawing Figures gri /tim PATENTEDAPR 18 I972 656,706

METERING VALVE INVENTOR BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a control device and, moreparticularly, to a piston follower device for use in controlapplicatrons.

2. Description of the Prior Art .The prior art is replete with a widevariety of control devices. Despite the wide and diverse varieties ofcontrol devices suggested, the prior art of which I am aware has notbeen satisfactory in providing a simple, ruggedly built piston followercontrol device that can be employed for simple on-off flow control oremployed to replace sophisticated controls in difficultly resolvablecontrol situations employing dynamic balancing of control elements.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view,partly schematic, of one embodiment of this invention.

FIG. 2 is a partial cross sectional view of another embodiment of thisinvention with the biasing means reversed.

FIG. 3 is a schematic side cross sectional view of another embodiment ofthis invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, pistonfollower device 11 includes a body 13 defining a control chamber 15and'a pilot chamber 17. A control piston 19 is disposed within controlchamber 15 and divides the control chamber into power end 21 and shaftend 23. Control piston 19 has appropriate seal means 25 for preventingfluid communication between the power end 21 and the shaft end 23.Control piston 19 also has a shaft 27 for connecting with a controlmeans. Control piston 19 has a larger surface exposed to fluid pressurein power end 21 than is exposed to fluid pressure in shaft end 23, sincethe shaft 27 reduces the area of the surface in shaft end 23. Controlpiston 19 also has a fluid passageway 29 therethrough. Fluid passageway29 communicates at its one end with the power end of the control chamberand at its other end with a source of fluid at a different pressure; forexample, with the downstream side of a valve means.

A pilot piston 31 is disposed within pilot chamber 17 and divides itinto a pilot pressure end 33 and a control pressure end 35 that is influid communication via aperture 37 with the power end 21 of controlchamber 15. Pilot piston 3l'includes a regulator surface portion 39 thatis positionable adjacent and near the one end of the fluid passagewaythat is in fluid communication with the power end of the controlchamber. Regulator surface portion 39 and the adjacent one end of fluidpassageway 29 define a flow restricting means such as outlet 41.

Annular passageway 43 intermediate shaft 27 and the wall of body 13defines a first fluid communication means for connecting the shaft end23 with a first source of fluid at a first pressure, referred to asfirst fluid pressure, to effect a pressure P,- within the shaft end ofthe control chamber.

Port 45 serves as a second fluid communication means for connecting thepower end 21 of the control chamber with a second fluid pressure. Thesecond fluid communication means may also include appropriate bushings,fittings, and conduit such as tubing or passageways through the valvebody; or other fluid flow means communicating between the power end 21and the second fluid pressure.

A third fluid communication means comprising second port 47 is providedfor connecting the pilot pressure end 33 with a third fluid pressure toeffect a pilot pressure within the pilot pressure end of the pilotchamber. The third fluid communication means may also includeappropriate bushings, fittings and conduit communicating between thepilot pressure end and. the third fluid pressure source.

A biasing means comprising spring 49 is disposed to act on the pilotpiston 31 so as to tend to force it toward an equilibriurn position. Asillustrated in FIG. 1, the equilibrium position tends to open outlet 41,reduce the control pressure in the power end 21 and effect movement ofthe control piston toward the control end, correspondingly positioningthe control means. As illustrated in FIG. 2, however, the biasing meansis reversed and tends to force the regulator surface portion 39 to closeoutlet 41. Closing outlet 41 raises the pressure in the power end 21 tothe pressure with which port 45 is connected, and, if great enough,tends to force control piston 19' toward the shaft end.

As illustrated, the control means comprises a valve means forcontrolling fluid flow. Specifically, the piston follower device 11includes an inlet passage 51 leading to an inlet chamber 53 and anoutlet passage 55 leading from an outlet chamber 57. Interposed betweenthe inlet and outlet chambers 53 and 57 is a wall structure 59 having anopening therein which serves as a valve aperture 61. Circumferentiallydisposed about valve aperture 61 on the inlet side is a valve seat 63. Apoppet valve portion 65 has a guiding skirt 67 slidably retained withinvalve aperture 61 and having slots therein defining a fluid flow path.The poppet valve portion 65 may be at any position between a fullyopened and a fully closed position. Depending upon the system in whichit is employed, poppet valve portion 65 may effect a fully openedposition for an equilibrium position or may effect a fully closedposition for an equilibrium position. The biasing means and therespective pressures will be disposed so as to create forces tending toposition the control piston and, consequently, the valve means in therespective equilibrium position; for example, tending to open the valvemeans as illustrated in FIG. 1, and tending to close the valve means asillustrated in FIG. 2.

If desired, a fluid flow passageway 69, dashed lines, FIG. 1, may beprovided in fluid communication between the pilot pressure end 33 andthe power end 21 for allowing fluid to flow therebetween. Fluid flowpassageway 69 has interposed therein a flow restricting device such asneedle valve 71 for controlling the rate at which fluid flows throughfluid flow passageway 69. Fluid flow passageway 69 enables dynamicpositioning of pilot piston 31 and through follower action controlpiston 19 at an intermediate position. Fluid flow passageway 69 alsoallows a smooth control transition to follow from an abrupt change ofeither the pilot pressure P in pilot end 33 or the control pressure I inpower end 21-.

Another embodiment of the invention is illustrated in FIG. 3. Theembodiment illustrated in FIG. 3 may be employed in difficult controlsituations formerly requiring much more elaborate and sophisticatedcontrol equipment. It also illustrates the range of utility in which thepiston follower device of the invention may be employed with only simplemodifications. Ordinarily, the modifications may be made in externalfluid communication means, although in FIG. 3 additional ports are shownfor simplicity of explanation. As indicated, in FIG. 3 the basicconstituents of the body, the chambers, and the respective pistons aremuch the same as illustrated and described in connection with FIG. 1.Accordingly, such description is not repeated herein, only thedifferences being noted. In FIG. 1, pilot piston 31 has a protrudingregulator surface portion 39 that extends into the power end 21 of thecontrol cylinder adjacent the one end of the fluid passageway 29,whereas in FIG. 3 fluid passageway 29 is extended via stern means 73 tonear regulator surface 39 in the control pressure end 35 of pilotchamber 17 to define the outlet 41.

As illustrated in FIG. 3, the piston follower device may be employed asan up control bypass valve in a system described in detail in mycopending application Ser. No. 885,736, entitled Control System forNeutralizing Effect of Load Variations on Operation of a HydraulicElevator, filed Dec. 17, I969. The detailed description of that elevatorcontrol system will not be repeated herein. The interconnection of therespective parts of the piston follower device will be described,however, with fluid flow being the same as is employed in an elevatorcontrol system for ensuring that a hydraulically powered elevator alwaysstops level with a given floor, regardless of the load interposedthereon or the speed at which the elevator is moving.

Specifically, in FIG. 3, a schematic illustration of theinterconnections of the elements in a working environment is shown. lnaddition to the elements previously described with respect to FIG. 1 andduplicated herein, a first fluid flow passageway 75 communicates betweena first source of fluid pressure and the pilot pressure end of the pilotchamber for effecting a pilot pressure and generating a first force onthe pilot piston for moving it in a first direction. The first fluidflow passageway 75 has first flow restricting means N-3 interposedtherein and is serially connected with second port 47 and third port 77.As illustrated, third port 77 communicates with the fluid pressure ininlet chamber 53 which serves as a first source of fluid pressure. Anyother source of fluid pressure which would effect the requisite pressurein power end 21 of control chamber 19 could be employed. The illustratedinter connection, however, eliminates the need for supplemental sourceof fluid pressure. A solenoid operated control valve SV3 is alsointerposed in first fluid flow passageway 75 for controlling flowthrough first fluid passageway 75 in response to a first control signalsuch as an electrical signal from a control switch (not shown).

A second fluid passageway 79 communicates via a second flow restrictingmeans N-6 between a second source of fluid pressure and the power end 21of control chamber for effeeling a control pressure therein. The controlpressure generates a second force on the pilot piston 31 for moving itin a second direction opposite to the first direction. It also generatesa force on control piston 19 tending to force it upwardly, or tending toclose the poppet valve portion 65 against valve seat 63. Specifically,second fluid passageway 79 has second flow restricting means N-6interposed therein and is serially connected with port 45 and third port77. As illustrated in FIG. 3, third port 77 is in fluid communicationwith inlet chamber 53 such that the second source of fluid pressure isthe same as the first source of fluid pressure. A different source offluid pressure can be employed, however, as long as it will effect therequisite force on the control piston and oppose the force on the pilotpiston. Fluid flow passageway 69 communicates via a third flowrestricting means N-4 between the pilot pressure end 33 and the powerend 21 for effecting dynamic positioning of the pilot piston and foreffecting a controlled response to a sudden change in one of thepressures in the cylinders; for example, the pilot pressure or thecontrol pressure. Fluid flow passageway 69 is illustrated as beingconnected between an additional set of ports. If desired, however, itmay be connected into first fluid flow passageway 75 and second fluidflow passageway 79 between any flow control or flow restricting meansand respective ports 47 and 45. Fluid flow passageway 69, in the contextof FIG. 3, may be thought of as a third fluid flow passageway.

A fourth fluid flow passageway 81 is provided communicating with anothersource of fluid at a fourth pressure and having a flow control meansinterposed therein for establishing a desired position of the pilotpiston 31; and, through follower co-action, of the control piston 19.For wide flexibility in obtaining a desired control of fluid flow,fourth fluid flow passageway 81 is operationally connectable with eithera low pressure source or a high pressure source of fluid. Expressedotherwise, fourth fluid flow passageway 81 is connected such thatmovement of pilot piston 31, and through follower action, movement ofcontrol piston 19 may be effected in either of two ways. First, in orderthat the pilot piston may be moved smoothly toward an equilibriumposition; such as that effecting the fully opened position of the valve;by opening a flow control valve, passageway 81 is connected to a sourceof lower pressure. This arrangement is illustrated by serially connectedline 83, solenoid valve SV-4, line 85, and return conduit 87 back to thefluid reservoir. Solenoid valve SV-4 is a controllable valve that can beactuated in response to an electrical signal from a suitable controlswitch (not shown).

Second, in order that pilot piston 31 and control piston 19 may bepositioned at a plurality of dynamically controlled positions,correspondingly positioning poppet valve portion 65 at a plurality ofpositions for effecting variable fluid flow,

' passageway 81 is connected with a source of high or variable pressure.This arrangement is illustrated by serially connected line 89, solenoidvalve SV-S, line 91, metering valve 93, check valve 96, and highpressure line from the pump to the elevator jack. Line 95 supplies highpressure hydraulic fluid to raise an elevator. Metering valve 93 isconnected into line 95 at check valve 96, and controls flow of fluidfrom line 95 into line 91 to keep some fluid moving through check valve96 for up levelling, as described in U.S. Pat. No. 3,266,382, entitledHydraulic Elevator Control System, patented Aug. 16, 1966 to R. F.Loughridge. It is sufiicient to say at this point that metering valve 93bleeds the high pressure hydraulic fluid into pilot pressure end 33 toprevent complete opening of poppet valve 65 and ensure that a smallamount of hydraulic fluid continues to flow throughcheck valve 96 aswill be apparent from the operational description hereinafter. Solenoidvalve SV-S is a controllable valve that is interposed in line 89 forcontrolling fluid flow therethrough in response to suitable signals suchas a signal from a control switch (not shown).

in operation, piston follower device 11 has great flexibility ineffecting the desired control in a wide variety of control situations.As illustrated in FIG. 1, for example, the piston follower device may beemplaced in a conduit to control fluid flow in response to differentcontrol variables. To illustrate, in a given liquid level controlsituation, it may be desirable to maintain both a differential head of asupernatant liquid 98, and a level of a heavier liquid 99; both of whichare being flowed via a conduit 97 into a vessel 103 wherein therespective fluid levels are to be controlled. Fluid conduit 97 may becarrying the admixture of liquids to the vessel 103. The vessel, ofcourse, would have the usual conduits and control valves for controllingthe efiluent flow of liquid from respective levels therein. With enoughsupernatant liquid in the vessel, the dilferential liquid levelcontroller 105 might send a pilot pressure signal to second port 47 todrive regulator surface portion 39 against the end of fluid passageway29 and cause the pressure in the power end 21 to be the same as beingsupplied by port 45. With sufficient control pressure, control piston 19would close the valve means and stop further flow into the vessel. Onthe other hand, if there is inadequate heavier liquid in the vessel, theliquid level controller 107 therefor will not effect closure of thevalve means. Specifically, the pressure at port 45 might be the pressurefrom the liquid level controller 107, which would be low. Accordingly,the control piston would not be moved toward the closed position untilthe control pressure in power end 21, the pressure from the liquid levelcontroller 107, was great enough to produce a force greater than thatproduced by the pressure in shaft end 23 acting on the reduced area ofthe control piston 19. Thus, liquid would continue to How into thevessel until the proper liquid level of the heavier liquid was alsoachieved. Thereafter, the pressure output from liquid level controller107 and, hence, the control pressure would be great enough to force thecontrol piston upwardly, closing the valve means.

Conversely, if the pressure from liquid level controller 107 were greatenough to cause the control piston to close poppet valve portion 65against seat 63, but there was inadequate supernatant liquid in thevessel, liquid should continue to flow into the vessel. Differentialliquid level controller 105 would lower its output such that thepressure would be reduced in pilot pressure end 33. The pilot piston 31would be moved toward pilot pressure end 33 by the control pressure inpower end 21 and the force of biasing means 49, opening outlet 41,reducing the pressure in power end 21 and allowing poppet valve 65 to beopened by movement of the control piston toward the power end. As thedifferential head of liquid builds and the pressure in pilot pressureend 33 increases, the regulator surface portion 39 is moved to close 011the outlet 41, allowing the control pressure in power end 21 to increaseand effect closure of poppet valve portion 65 by the desired movement ofcontrol piston 19.

As can be seen from the operational sequence described above, a simplecontrol is effected in response to a dual parameter control system. Ifdesired, smoother control can be effected by the inclusion of the fluidflow passageway 69 with its adjustable flow restricting means such asneedle valve 71 therein. That is, a sudden change in either the pilotpressure or the control pressure would not effect so drastic a change inmovement of either pilot piston 31 or control piston 19 because thepressure would build up in either the power end or the piston end moregradually since fluid would be bled at a controlled rate into theopposing end. The bypass arrangement afforded by fluid flow passageway69 in conjunction with the biasing means affects a fail-safe arrangementwhich will position the valve means at the desired equilibrium positionin the event of a malfunction. In FIG. 1, for example, if the controlpressure becomes as great as the pilot pressure, the valve means willopen to keep liquid flowing into the vessel 103. This arrangement wouldbe desirable where one of the liquids served as feed for another unitand a minimum level was vital to a large process.

As illustrated, the biasing means such as spring 49 co-acts with thepressure in power end 21 to tend to force pilot piston 31 toward pilotpressure end 33, thereby opening the valve means in the equilibriumposition. There may be instances where the equilibrium position that isdesired is with the valve closed. In such instances, the biasing meansmay be reversed as indicated in FIG. 2. As illustrated therein, thepilot piston 31 is biased to move toward and close outlet 41 in thepower end such that the pressure in the power end would go to themaximum control pressure and would, consequently, tend to close poppetvalve 65 against valve seat 63 in the equilibrium position. Theembodiment chosen will depend on what position of the valve is desiredin emergencies, commonly referred to as the fail-safe" position. Thefluid flow passageway 69 may be incorporated into the embodiment of FIG.2, if desired, to allow the same smoother response to variations in thecontrol pressure or pilot pressure and equilibrium positioning of thevalve. Fluid flow passageway 69 may be employed in conjunction with acheck valve in one control line to allow the other control parameter toultimately effect closure of the valve by equalizing the pilot pressureand the control pressure.

In operation of the embodiment of FIG. 3, the piston follower device isemployed as an up control bypass valve in a hydraulic elevator controlsystem similar to that described in a plurality of patents; for example,U.S. Pat. No. 3,065,738; U.S. Pat. No. 3,141,383; and U.S. Pat. No.3,266,382, issued to R. F. Loughridge and U.S. Pat. No. 3,438,398,issued to Everett E. Johnston; and specifically described in myaforementioned copending application Ser. No. 885,736. It is sufficientto note, that operation of the piston follower device of F IG. 3controls the valve means through which hydraulic fluid is being bypassedfrom inlet conduit 97, connected in parallel with a hydraulic jackcontrolling movement of an elevator. The hydraulic fluid is bypassedinto return conduit 87 for return to the reservoir when the elevator isnot being raised. Thus, in the equilibrium position, poppet valve 65 isfully opened and all of the fluid is being returned to the reservoirwhile the fluid in the hydraulic jack controlling the elevator is heldby check valve 96.

To start a cycle of movement upwardly, the up button switch or selectedfloor button switch in the elevator (not shown) is depressed. Solenoidvalve SV-4 closes, which prevents the fluid from flowing through dumplines 83 and 85 to return conduit 87. Solenoid valve SV-S also closes,preventing fluid flow through line 89. Solenoid valve SV-3 opens,allowing the fluid to flow through first fluid flow passageway 75 andflow restricting means N-3 into second port 47. Fluid also flows throughsecond fluid flow passageway 79 and flow restricting means N-6 into port45. There is a tendency for the pressure in pilot pressure end 33 andcontrol pressure end 35 to balance by way of third fluid flow passageway69 and needle valve N-4. More than ofisetting this tendency to balance,however, is outlet 41 which allows fluid to flow from control pressureend and power end 21, through passageway 29 to outlet chamber 57,consequently lowering the control pressure. When the higher pressure inpilot pressure end 33 becomes great enough to overcome the force ofspring 49, pilot piston 31 is moved upwardly in FIG. 3, moving pressureregulator portion 39 closer to the end of passageway 29, reducing theoutlet 41. When outlet 41 is small enough and sufficiently reduces theescape of fluid from power end 21, the pressure increases and begins toforce control piston 19 toward the closed position. Pilot piston 31 andcontrol piston 19 move in piston-follower relationship because of therespective pressure forces as delineated hereinbefore. Movement ofcontrol piston 19, moves valve portion 65 toward valve seat 63,ultimately effecting a fully closed aperture and all of the fluid isbeing employed in the hydraulic jack to raise the elevator. Even whenthe valve means is fully closed, however, a small opening at outlet 41will still allow a bleed-off of a small amount of fluid to balance theeffects of spring 49. Thus, the pilot piston is retained in dynamicbalance.

The elevator is thus moving upwardly at full speed. As it approaches adesired destination floor, a deceleration phase is initiated by asuitable cam actuating a suitable switch means (not shown). Actuation ofthe switch means closes solenoid valve SV-3 and opens solenoid valveSV-S. Closure of solenoid valve SV-3 prevents further fluid flow intopilot pressure end 33 and pressure tends to equalize by way of thirdfluid flow passageway 69 and needle valve N-4. Consequently, spring 49moves pilot piston 31 downwardly, enlarging the outlet 41. The largeroutlet 41 allows a greater volume of fluid to flow out fluid passageway29, reducing the pressure in the power end 21 of control chamber 15 andacting on control piston 19. Thus, control piston 19 will movedownwardly, or toward power end 21, opening the aperture effectedbetween poppet valve portion 65 and seat 63. The rate of deceleration iscontrolled by adjusting needle valve N4 in third fluid flow passageway69.

The solenoid valve SV-S and fourth fluid flow passageway 81 are employedto effect an up levelling phase in the elevator control cycle. They maybe employed to control fluid flow responsive to almost any variable.When the switch means is actuated by the cam, solenoid valve SV-S isopened, and fluid is supplied from check valve 96 via metering valve 93and line 91 to pilot pressure end 33. This added pressure serves toretain pilot piston 31 at some intermediate position which retains somefluid flowing through the check valve to the hydraulic jack so that theelevator car continues to move upwardly with a constant up levellingspeed as described in connection with the copending application Ser. No.885,736 and in U.S. Pat. No. 3,266,382, referred to hereinbefore.

The elevator will continue to move upwardly at a constant up levellingspeed until the desired destination floor is reached, at which time thesolenoid valve SV-4 is opened, inter alia. The opening of solenoid valveSV-4 dumps fluid from the pilot pressure end 33, opens the bypass valve,and stops the elevator. The piston follower device is again ready foranother cycle of upward movement if it is desired to proceed to anotherhigher floor.

Thus, it can be seen that the piston follower device of the inventionhas application in a wide variety of situations. It is simple andruggedly constructed and may be employed in difflcultly accessibleenvironments since it is trouble-free in operation.

Certain of the terms employed herein have been exemplified by narrowembodiments and a brief consideration of broader implications may behelpful. As illustrated, the pilot piston has equal areas subjected tothe respective fluid pressures such that when the pressures on bothsides thereof are equal the response of the pilot piston is governed bythe spring constant, or a predictable response of the biasing means.Different areas may be employed if desired.

Although pilot and control pistons have been described herein, the tennpiston, is employed in a generic sense to represent any body, includingdiaphram structures serving as thin pistons, that are subjected to andmoved in response to fluid pressure and forces derived from system fluidpressure and modified as described hereinbefore. Also, fluid flowpassageway, and the like include equivalent structures.

Although the present invention has been described with a certain degreeof particularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of the invention.

What is claimed is:

l. A piston follower device comprising:

a. a body having a control chamber therein;

b. a control piston disposed within said control chamber and having ashaft for connecting with a control means; said control piston dividingsaid control chamber into a power end and a shaft end and having alarger surface exposed to fluid pressure in said power end that isexposed to fluid pressure in said shaft end; said control piston alsohaving therethrough a fluid passageway for communicating at one end withsaid power end and at the other end with a source of fluid at adifferent pressure;

c. a pilot chamber in fluid communication with said power end;

d. a pilot piston disposed within said pilot chamber and dividing saidpilot chamber into a pilot pressure end, and a control pressure end thatis in fluid communication with said power end of said control chamber;said pilot piston including a regulator surface portion that ispositionable adjacent and near said one end of said fluid passagewaythrough said control piston to define a flow restricting means;

e. first fluid communication means for connecting said shaft end with afirst fluid pressure to effect a pressure P, therewithin;

f. second fluid communication means for connecting said power end with asecond fluid pressure tending to effect a control pressure therewithin;

g. third fluid communication means for connecting said pilot pressureend with a third fluid pressure to effect a pilot pressure therewithin;I

h. fourth fluid communication means between said pilot pressure end andsaid power end having interposed therein a flow restricting device foreffecting a dynamic balance on said pistons and for effecting acontrolled response to a sudden change of one of the pressures, controlpressure and pilot pressure; and

i. biasing means disposed to act on said pilot piston and tending toforce it to an equilibrium position; whereby when connected with therespective fluid pressures said pilot piston is positioned by forces,including pilot pressure, said biasing means and control pressure, withits regulator surface portion defining said flow restricting means withsaid one end of said fluid passageway; said flow restricting means beingadapted to coact with said second fluid communication means to effect acontrol pressure in said power end and, consequently, in said controlpressure end, and by follower action effect a corresponding position ofsaid control piston.

2. A piston follower device comprising:

a. a body having a control chamber therein;

b. a control piston disposed within said control chamber and having ashaft for connecting with a valve means; said control piston dividingsaid control chamber into a power end and a shaft end and having alarger surface exposed to fluid pressure in said power end than isexposed to fluid pressure in said shaft end; said control piston alsohaving therethrough a fluid passageway for communicating at one end withsaid power end and at the other end with a source of fluid at a pressurewhich is less than the fluid pressure on the upstream side of said valvemeans;

c. a pilot chamber in fluid communication with said power end;

d. a pilot piston disposed within said pilot chamber and dividing saidpilot chamber into a pilot pressure end, and

a regulator surface portion that is positionable adjacent and near saidone end of said fluid passageway through said control piston to define aflow restricting means;

e. first fluid communication means for connecting said shaft end with afirst fluid pressure, which is the fluid pressure on the upstream sideof said valve means, to effect a pressure P, therewithin;

f. second fluid communication means for connecting said power end with asecond fluid pressure tending to effect a control pressure therewithin;

g. third fluid communication means for connecting said pilot pressureend with a third fluid pressure to effect a pilot pressure therewithin;and

h. biasing means disposed to act on said pilot piston and tending toforce it to an equilibrium position; whereby when connected with therespective fluid pressures said pilot piston is positioned by forces,including pilot pressure, said biasing means and control pressure, withits regulator surface portion defining said flow restricting means withsaid one end of said fluid passageway; said flow restricting means beingadapted to coact with said second fluid communication means to effect acontrol pressure in said power end and, consequently, in said controlpressure end, and by follower action effect a corresponding position ofsaid control piston.

3. The piston follower device of claim 2 wherein said biasing means isdisposed to act on said pilot piston so as to force it toward said pilotpressure end for increasing the flow of fluid through said fluidpassageway for effecting movement of said control piston toward saidpower end.

4. The piston follower device of claim 2 wherein said biasing means isdisposed to act on said pilot piston so as to force it toward saidcontrol pressure end for decreasing the flow of fluid through said fluidpassageway for effecting movement of said control piston toward saidshaft end.

5. A piston follower device comprising:

a. a body having an inlet passage and an inlet chamber for connectionwith a high pressure source of fluid, and having an outlet passage andan outlet chamber for connection with a low pressure source of fluid;

b. wall structure intermediate said inlet chamber and said outletchamber and having an aperture communicating therebetween and having avalve seat therearound;

c. valve portion disposed adjacent said valve seat, operable to controlflow of fluid through said aperture by being moved with respect to saidvalve seat;

d. control chamber in fluid communication with said inle chamber;

e. control piston disposed within said control chamber and connected viaa shaft with said valve portion so as to position said valve portionwith respect to said valve seat; said control piston dividing saidcontrol chamber into a power end, and a shaft end that is in fluidcommunication with said inlet chamber, and having a larger surfaceexposed to fluid pressure in said power end than is exposed to fluidpressure in said shaft end; saidcontrol piston also having therethrougha fluid passageway that communicates at one end with said outletchamber;

f. a pilot chamber in fluid communication with said power end; i

g. a pilot piston'disposed within said pilot chamber; dividing saidpilot chamber into a pilot pressure end and a control pressure end thatis in fluid communication with said power end; said pilot pistonincluding a regulator surface portion that is positionable adjacent andnear said one end of said fluid passageway through said control pistonto define a flow restricting means;

h. first fluid flow passageway communicating via a first flowrestricting means between a first source of fluid pressure and saidpilot pressure end of said pilot chamber for effecting a pilot pressureand generating a first force on said pilot piston for moving it in afirst direction;

i. second fluid passageway communicating via a second flow restrictingmeans between a second source of fluid pressure and said power end ofsaid control chamber for effecting a control pressure generating a forceon said control piston and generating a second force on said pilotpiston for moving it in a second direction opposite said firstdirection;

j. biasing means disposed to act on said pilot piston so as to effect anequilibrium position thereof; whereby said pilot piston is positioned inaccordance with the forces generated by said first and second forces andsaid biasing means with its regulator surface portion defining said flowrestricting means with said one end of said fluid passageway; said flowrestricting means co-acting with said second flow restricting means toeffect a control pressure in said power end and, consequently, saidcontrol pressure end, and by follower action effect a correspondingposition of said control piston and said valve portion.

6. The piston follower device of claim wherein a third fluid flowpassageway is provided communicating via a third flow restricting meansbetween said pilot pressure end and said power end for effecting dynamicpositioning of said pilot piston and for effecting a controlled responseto a sudden change in one of said pilot pressure and said controlpressure.

7. The piston follower device of claim 5 wherein said first source offluid pressure and said second source of fluid pressure are both influid cormnunication with said inlet chamber; a third fluid flowpassageway is provided communicating via a third flow restricting meansbetween said pilot pressure end and said power end; and a fourth fluidflow passageway is provided communicating with another source of fluidat a different pressure and having a flow control means interposedtherein for establishing a dynamic balance on said pilot piston andthrough follower co-action between said regulator surface portion ofsaid pilot piston and said one end of said fluid passageway through saidcontrol piston establishing a dynamic balance on said control piston.

8. The flow control device of claim 5 wherein said control piston has astem means defining said fluid passageway, said stem means extending thefluid passageway to near said regulator surface portion of said pilotpiston in said control pressure end of said pilot chamber.

9. The piston follower device of claim 5 wherein said pilot piston has aprotruding regulator surface portion that extends into said power end ofsaid control cylinder adjacent said one end of said fluid passageway.

10. The piston follower device of claim 5 wherein said biasing means isdisposed to act on said pilot piston so as to force it toward the pilotpressure end so as to tend to position said valve portion in the openposition.

1 l. The piston follower device of claim 5 wherein said biasing means isdisposed to act on said pilot piston so as to force it toward thecontrol pressure end so as to tend to position the valve portion in theclosed position.

nun-ya mun

1. A piston follower device comprising: a. a body having a controlchamber therein; b. a control piston disposed within said controlchamber and having a shaft for connecting with a control means; saidcontrol piston dividing said control chamber into a power end and ashaft end and having a larger surface exposed to fluid pressure in saidpower end that is exposed to fluid pressure in said shaft end; saidcontrol piston also having therethrough a fluid passageway forcommunicating at one end with said power end and at the other end with asource of fluid at a different pressure; c. a pilot chamber in fluidcommunication with said power end; d. a pilot piston disposed withinsaid pilot chamber and dividing said pilot chamber into a pilot pressureend, and a control pressure end that is in fluid communication with saidpower end of said control chamber; said pilot piston including aregulator surface portion that is positionable adjacent and near saidone end of said fluid passageway through said control piston to define aflow restricting means; e. first fluid communication means forconnecting said shaft end with a first fluid pressure to effect apressure Pi therewithin; f. second fluid communication means forconnecting said power end with a second fluid pressure tending to effecta control pressure therewithin; g. third fluid communication means forconnecting said pilot pressure end with a third fluid pressure to effecta pilot pressure therewithin; h. fourth fluid communication meansbetween said pilot pressure end and said power end having interposedtherein a flow restricting device for effecting a dynamic balance onsaid pistons and for effecting a controlled response to a sudden changeof one of the pressures, control pressure and pilot pressure; and i.biasing means disposed to act on said pilot piston and tending to forceit to an equilibrium position; whereby when connected with therespective fluid pressures said pilot piston is positioned by forces,including pilot pressure, said biasing means and control pressure, withits regulator surface portion defining said flow restricting means withsaid one end of said fluid passageway; said flow restricting means beingadapted to coact with said second fluid communication means to effect acontrol pressure in said power end and, consequently, in said controlpressure end, and by follower action effect a corresponding position ofsaid control piston.
 2. A piston follower device comprising: a. a bodyhaving a control chamber therein; b. a control piston disposed withinsaid control chamber and having a shaft for connecting with a valvemeans; said control piston dividing said control chamber into a powerend and a shaft end and having a larger surface exposed to fluidpressure in said power end than is exposed to fluid pressure in saidshaft end; said control piston also having therethrough a fluidpassageway for communicating at one end with said power end and at theother end with a source of fluid at a pressure which is less than thefluid pressure on the upstream side of said valve means; c. a pilotchamber in fluid communication with said power end; d. a pilot pistondisposed within said pilot chamber and dividing said pilot chamber intoa pilot pressure end, and a regulator surface portion that ispositionable adjacent and near said one end of said fluid passagewaythrough said control piston to define a flow restricting means; e. firstfluid communication means for connecting said shaft end with a firstfluid pressure, which is the fluid pressure on the upstream side of saidvalve means, to effect a pressure Pi therewithin; f. second fluidcommunication means for connecting said power end with a second fluidpressure tending to effect a control pressure therewithin; g. thirdfluid communication means for connecting said pilot pressure end with athird fluid pressure to effect a pilot pressure therewithin; and h.biasing means disposed to act on said pilot piston and tending to forceit to an equilibrium position; whereby when connected with therespective fluid pressures said pilot piston is positioned by forces,including pilot pressure, said biasing means and control pressure, withits regulator surface portion defining said flow restricting means withsaid one end of said fluid passageway; said flow restricting means beingadapted to coact with said second fluid communication means to effect acontrol pressure in said power end and, consequently, in said controlpressure end, and by follower action effect a corresponding position ofsaid control piston.
 3. The piston follower device of claim 2 whereinsaid biasing means is disposed to act on said pilot piston so as toforce it toward said pilot pressure end for increasing the flow of fluidthrough said fluid passageway for effecting movement of said controlpiston toward said power end.
 4. The piston follower device of claim 2wherein said biasing means is disposed to act on said pilot piston so asto force it toward said control pressure end for decreasing the flow offluid through said fluid passageway for effecting movement of saidcontrol piston toward said shaft end.
 5. A piston follower devicecomprising: a. a body having an inlet passage and an inlet chamber forconnection with a high pressure source of fluid, and having an outletpassage and an outlet chamber for connection with a low pressure sourceof fluid; b. wall structure intermediate said inlet chamber and saidoutlet chamber and having an aperture communicating therebetween andhaving a valve seat therearound; c. valve portion disposed adjacent saidvalve seat, operable to control flow of fluid through said aperture bybeing moved with respect to said valve seat; d. control chamber in fluidcommunication with said inlet chamber; e. control piston disposed withinsaid control chamber and connected via a shaft with said valve portionso as to position said valve portion with respect to said valve seat;said control piston dividing said control chamber into a power end, anda shaft end that is in fluid communication with said inlet chamber, andhaving a larger surface exposed to fluid pressure in said power end thanis exposed to fluid pressure in said shaft end; said control piston alsohaving therethrough a fluid passageway that communicates at one end withsaid outlet chamber; f. a pilot chamber in fluid communication with saidpower end; g. a pilot piston disposed within said pilot chamber;dividing said pilot chamber into a pilot pressure end and a controlpressure end that is in fluid communication with said power end; saidpilot piston including a regulator surface portion that is positionableadjacent and near said one end of said fluid passageway through saidcontrol piston to define a flow restricting means; h. first fluid flowpassageway communicating via a first flow restricting means between afirst source of fluid pressure and said pilot pressure end of said pilotchamber for effecting a pilot pressure and generating a first force onsaid pilot piston for moving it in a first direction; i. second fluidpassageway communicating via a second flow restricting means between asecond source of fluid pressure and said power end of said controlchamber for effecting a control pressure generating a force on saidcontrol piston and generating a second force on said pilot piston formoving it in a second direction opposite said first direction; j.biasing means disposed to act on said pilot piston so as to effect anequilibrium position thereof; whereby said pilot piston Is positioned inaccordance with the forces generated by said first and second forces andsaid biasing means with its regulator surface portion defining said flowrestricting means with said one end of said fluid passageway; said flowrestricting means co-acting with said second flow restricting means toeffect a control pressure in said power end and, consequently, saidcontrol pressure end, and by follower action effect a correspondingposition of said control piston and said valve portion.
 6. The pistonfollower device of claim 5 wherein a third fluid flow passageway isprovided communicating via a third flow restricting means between saidpilot pressure end and said power end for effecting dynamic positioningof said pilot piston and for effecting a controlled response to a suddenchange in one of said pilot pressure and said control pressure.
 7. Thepiston follower device of claim 5 wherein said first source of fluidpressure and said second source of fluid pressure are both in fluidcommunication with said inlet chamber; a third fluid flow passageway isprovided communicating via a third flow restricting means between saidpilot pressure end and said power end; and a fourth fluid flowpassageway is provided communicating with another source of fluid at adifferent pressure and having a flow control means interposed thereinfor establishing a dynamic balance on said pilot piston and throughfollower co-action between said regulator surface portion of said pilotpiston and said one end of said fluid passageway through said controlpiston establishing a dynamic balance on said control piston.
 8. Theflow control device of claim 5 wherein said control piston has a stemmeans defining said fluid passageway, said stem means extending thefluid passageway to near said regulator surface portion of said pilotpiston in said control pressure end of said pilot chamber.
 9. The pistonfollower device of claim 5 wherein said pilot piston has a protrudingregulator surface portion that extends into said power end of saidcontrol cylinder adjacent said one end of said fluid passageway.
 10. Thepiston follower device of claim 5 wherein said biasing means is disposedto act on said pilot piston so as to force it toward the pilot pressureend so as to tend to position said valve portion in the open position.11. The piston follower device of claim 5 wherein said biasing means isdisposed to act on said pilot piston so as to force it toward thecontrol pressure end so as to tend to position the valve portion in theclosed position.